The present invention relates to the axial seals and radial seals of a rotary regenerative air preheater for controlling leakage within the air preheater. More particularly, the invention relates methods and apparatus for adding additional axial seals and radial seals within installed air preheaters.
A rotary regenerative air preheater transfers sensible heat from the flue gas leaving a boiler to the entering combustion air through regenerative heat transfer surface in a rotor which turns continuously through the gas and air streams. The rotor, which is packed with the heat transfer surface, is divided into compartments by a number of radially extending plates referred to as diaphragms. These compartments are adapted to hold modular baskets in which the heat transfer surface is contained.
The air preheater is divided into a flue gas side or sector and one or more combustion air sides or sectors by sector plates. In a typical installed rotary regenerative heat exchanger, rigid or flexible radial seals mounted on the top and bottom edges of the diaphragms are in close proximity to these sector plates and minimize leakage of air and/or gas between sectors. Similarly, rigid or flexible axial seals mounted on the outboard edge of the diaphragms are in close proximity to axial seal plates mounted on the inner surface of the housing and minimize leakage therebetween. In typical installed air preheaters, the number of diaphragms and the width of the sector plates and the seal plates are such that only one radial seal and one axial seal is disposed proximate to the respective plate at any one time. These seals are proximity seals and are not designed to contact the sealing surface of the sector plates or seal plates. Consequently, there is leakage past the seals where the amount of leakage is dependent on the pressure differential between the air and gas streams across the seals. Leakage can degrade thermal performance and require increased energy use resulting in higher costs for powering the fans. The leakage flow carries ash which produces erosion of the seals and sealing surfaces.
The present invention relates to a method for adding additional axial seals and radial seals within existing air preheaters. To retrofit the additional seals, the original heat transfer baskets, the original radial seals, the original axial seals, and the original gratings are all removed from the air preheater. If the original stay plates are not to be re-used, they are removed. If the original stay plates are to be re-used, a strip of material is removed from the outer stay plates to accept an intermediate diaphragm plate, hot and cold extension plates are mounted on the inner stay plates. At this point an intermediate diaphragm plate is positioned within each original compartment and mounted to the inner and outer stay plates. Cold extension plates are then mounted on the outer stay plates. New gratings are mounted to the original diaphragm plates and the intermediate diaphragm plate if the basket supports comprise a combination of gratings and stay plates. Additional hot and cold end axial seal support bars are mounted to the rotor shell and intermediate diaphragm plate. Axial seals are installed on the original axial seal support bars and on the additional axial seal support bars and radial seals are installed on the axial edges of the original diaphragm plates and the intermediate diaphragm plates. Finally, new heat transfer baskets are inserted into each of the compartments formed by the original diaphragm plates, the intermediate diaphragm plates, and the rotor shell.